German Patent DE 4,013,760 C2 (Manzei) discloses an apparatus for the extruding of paste-like sludge material in the form of small sausage-shaped blanks. Extruders of this type are equipped with a plurality of extrusion holes that are provided as through-holes in a so-called matrix or screen having an upper screen section and a lower screen section. These through-holes have a tendency to clog, thereby reducing the efficiency since frequent stops are needed for cleaning of the screen. The German Patent DE 4,013,760 C2 teaches constructing the upper screen section as a shearing plate that cooperates with the lower screen section in severing the blanks from the extrudate. The cutting of precise and uniform blank lengths is not necessarily possible in the known device. Due to the shearing movement of the upper screen section functioning as a shearing plate, it is possible to shear materials in the sludge that are not moldable into the desired blanks. For this purpose the shearing plate or upper screen oscillates back and forth substantially in the same manner as in known pelletizers which employ a shearing plate for cutting off pellets from the extrudate. The lower screen section is stationary and the upper screen section functioning as the screening plate is driven by a suitable oscillator drive. Two oscillating screen sections may sandwich a stationary screen section between the oscillating screen section so that the entire screen is reversible. Even so, clogging cannot be avoided.
The just described apparatus of German Patent DE 4,013,760 C2 is not free of clogging problems and when clogging occurs the apparatus must be stopped for a cleaning operation. Thus, it is not possible to perform a cleaning operation while continuing the production of sausage-shaped blanks. Accordingly, a substantially continuous operation is not assured. This leaves room for improvement.